Many surgical procedures are planned and guided using images obtained from imaging systems such as magnetic resonance imagers (MRIs), computer tomographic imagers (CTs), x-ray imagers, positron emission tomographic (PET) scanners, and photo-emission computer technology (SPECT). These systems permit physicians to obtain detailed preoperative (or intraoperative) views of anatomical structures using noninvasive procedures. Once these images are obtained, the physician typically uses the images to plan a corrective surgical procedure. With the patient lying on an operating table, the images may be “registered” with the corresponding physical space of the patient, and displayed on a screen in the operating room (OR). As the physician navigates probes or other medical instruments within the patient, sensors on the instruments relay positional information to a computer. The computer, in turn, overlays a display of the position of the instrument on the image of the anatomical structure. In this way, the physician may navigate through a surgical procedure by viewing a display screen in the OR. An example of a related art system is found in U.S. patent application Ser. No. 08/809,404, now U.S. Pat. No. 6,236,875, entitled: “Surgical Navigation System Including Reference and Localization Frame,” and which is fully incorporated herein by reference.
Until now, the tracking of anatomical structures has been largely limited to external tracking, either by taping a sensor to a patient's skin, or by affixing an external clamp to the patient, such as a Mayfield clamp, attached externally to a patient's head.
U.S. patent application Ser. No. 08/931,654, now U.S. Pat. No. 6,347,240, entitled “Bone Navigation System” which is incorporated fully herein by reference discloses a system which employs screws extending from a bone fragment through a patient's skin and connected to a platform external to the patient. Tracking elements such as, for example, emitters are located on the platform so that when a bone fragment moves, so too does the platform with the connected tracking elements. An array in the OR tracks movement of the tracking elements, and this movement is correlated to the movement of the bone fragment, in order to precisely track the movement of the bone fragment. Alternatively, clamps may be used, in place of screws, to secure an array of tracking elements to a bone structure. While such related art systems may generally be reliable, their structure is somewhat cumbersome, especially when the movement of multiple anatomical structures needs to be tracked. In addition, the use of the tracking elements and receiving array requires an unobstructed line of sight therebetween which not only limits implantation within a patient, but also can lead to interference.
For these reasons, in procedures such as those involving the spine or the reconstruction or repair of vertebral bodies, fractured skulls, fragmented bones, or other damaged boney structures, it has been somewhat difficult to track the relative movement of multiple anatomical structures.